This invention relates generally to motive power systems and more particularly to systems for speed regulation of a motor in response to a resultant error signal.
Control of power application to vehicles powered by electromotive means is commonly accomplished by deriving an analog voltage signal proportional to motor speed and comparing it with an analog reference signal to produce an error signal which is in turn applied to the regulating system to change the motor speed. This change tends to bring the vehicle actual speed into conformance with the vehicle desired speed. Since the accuracy of a typical analog system decreases as the speed decreases, and since a weak signal at low speeds results in a slot reaction, such a system is not satisfactory for low speed operation.
An alternative method well known in the art is that of using a digital tachometer whose output signal frequency is proportional to velocity and whose accuracy is fixed irrespective of vehicle speed. The signal of constant width pulses is filtered and the resulting d-c signal is compared with a reference voltage to generate an error signal to the motor. Since the width of the pulses are constant throughout the speed range of the vehicle and since it is necessary to use narrow pulses to accommodate high frequencies, then at low frequencies the accuracy is necessarily depreciated. In certain instances this may be of great concern, as for example, when maintaining creep control at speeds of approximately one-half mile per hour during the loading of coal into a vehicle.
It is therefore an object of this invention to provide a speed regulation system for vehicles operating at low speed ranges.
Another object of this invention is the provision for a speed regulation system which is accurate at very low speeds and is capable of effective speed regulation at higher speeds.
Yet another object of this invention is the provision for a speed regulation system which is equally sensitive and accurate over a range of low speeds.
Still another object of this invention is the provision for a speed regulation system which is economical to manufacture and effective in use.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.